These guys claim >40degC, and are deploying in Dubai..

https://www.i2cool.com/tideflow/uwJVdixI.html

https://baitykool.com/radiativeskycooling.html

Peak performance, I think. Considering that they got the black white sides flipped

I didn't do the measurment and it's been a while so it's possible I misremembered the temperature delta, or maybe it was degrees F. It was about a 2-3 square meter sheet and it made about a liter of water overnight.